| Year | Value | | 2021 | 8.5654927672956 | | 2020 | 8.9204716981132 | | 2019 | 9.2754716981132 | | 2018 | 9.6304402515723 | | 2017 | 9.9854402515723 | | 2016 | 10.340440251572 | | 2015 | 10.695440251572 | | 2014 | 11.050427672956 | | 2013 | 11.40541509434 | | 2012 | 11.760402515723 | | 2011 | 12.115389937107 | | 2010 | 12.470377358491 | | 2009 | 12.825367924528 | | 2008 | 13.180358490566 | | 2007 | 13.535349056604 | | 2006 | 13.890339622642 | | 2005 | 14.245330188679 | | 2004 | 14.600320754717 | | 2003 | 14.955311320755 | | 2002 | 15.310301886792 | | 2001 | 15.66529245283 | | 2000 | 16.020283018868 | | 1999 | 16.887078616352 | | 1998 | 17.753874213837 | | 1997 | 18.620669811321 | | 1996 | 19.487465408805 | | 1995 | 20.354261006289 | | 1994 | 21.221056603774 | | 1993 | 22.087852201258 | | 1992 | 22.954647798742 | | 1991 | 23.821443396226 | | 1990 | 24.688238993711 |
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